1. Field of the Invention
The present invention relates to a method for preparing .beta.-chloropivaloyl chloride by the chlorination of pivalic acid.
2. Description of the Prior Art
.beta.-Chloropivaloyl chloride (.alpha.,.alpha.-dimethyl-.beta.-chloropropionyl chloride) is important as an intermediate for the synthesis of various compounds. Specifically, it is useful for the synthesis of, for example, pesticides. Japanese Patent Publication No. 46046/1972 describes a method of preparing .beta.-chloropivalic acid. According to this method, a chlorine gas is introduced into a distillation tower to contact with liquid phase pivalic acid, while the latter is refluxed in the distillation tower, and the resultant .beta.-chloropivalic acid is collected on the bottom of the tower by means of a distillation effect, followed by removing the product. Then, .beta.-chloropivalic acid may be allowed to react with phosgene, thionyl chloride or the like, thereby forming .beta.-chloropivaloyl chloride.
The above mentioned method for preparing .beta.-chloropivalic acid in Japanese Patent Publication No. 46046/1972 produces a smaller amount of dichloro-compounds and is considered to be superior, as compared with another method of directly blowing chlorine into pivalic acid. From the viewpoint of an industrial practice, however, this method has problems such as a temperature rise of up to 222.degree. C. on a tower bottom, the installation of a reaction apparatus using a specific heat transfer medium, the formation of decomposition products and polymers due to the heat history of the reaction solution, and the like.
When it is attempted to carry out the operation under a reduced pressure for the purpose of solving these problems, there will occur other problems of the treatment of a hydrogen chloride gas evolved during the reaction and the material quality for a vacuum generator required.
Therefore, in order to industrially synthesize .beta.-chloropivaloyl chloride with a high selectivity, the reaction must be carried out at a high temperature.
Further, in the method described in Japanese Patent Publication No. 46046/1972, the reaction rate of a clorination on side chains is slow, and thus, this method is not considered to be effective on the whole as the process for preparing .beta.-chloropivaloyl chloride.